Elevators and/or spiders are essentially functionally identical gripping devices used cooperatively to hold and lower drill pipe or tubular well casing into a well bore. These tools have varied over the years, but their essential overall design and function has remained the same. Elevator and spider slip assemblies conventionally have hinged arms that latch at the unhinged ends. With arms apart, they are placed around a given section of the tubing in a tubing string, then the arms are hinged closed and latched, forming a housing surrounding the tubing. The housing is commonly referred to as a “bowl”. The bowl contains a plurality of slips surrounding the tubing. The radial interior surface of the slips typically form or carry hard metal teeth for gripping the tubing. The exterior surface of the slips and interior surface of the bowl usually have opposing complementary engagement surfaces which are inclined radially inward and downwardly. The complementary surfaces between the slips and bowl serve to inject the slip and gripping elements in a longitudinal and radial direction in relation to the tubing for engagement or disengagement of the tubing. Thus, when an elevator or slip is engaged about a tubing and the weight of the tubing in the tubing string is lowered into the elevator or slip, the tubing engages the gripping elements on the slips, causing them to move downward in relation to the bowl and radially inward in a “self-tightening” securing of the tubing.
During traditional well-boring operations, a spider is located near the rotary table and is used for securing tubing in the well. An elevator is suspended from the rig hook, which is used for running or retrieving the tubing string. In a typical operation, the spider remains stationary to fix the tubing, while the elevator is lowered and placed around the tubing and engages the tubing by “self tightening”. The spider then disengages from the tubing when the slips are radially removed away from the tubing string, allowing the elevator to move the tubing string relative to the rotary table as needed. The spider then re-engages the tubing, allowing the elevator to continue running or removing the tubing string.
A problem associated with the use of these tools is related to gripping the drill pipe or casing collar which is of a larger diameter than the outside diameter of the body of the tubing. The problem is caused when the elevator slip assembly is not lowered sufficiently below the collar (including, in the case of drill pipe, the portion of the pipe transitioning from the exterior of the well casing below the collar to the maximum exterior diameter of the collar, sometimes called the “upset”). The slip assemblies are designed such that the gripping forces generated are sufficient for proper gripping only when the slips are lowered far enough below a casing collar to completely grip the outside diameter of the well casing and not the collar. When the collar is gripped, the slips will not engage with the casing sufficiently to generate adequate gripping forces. The result is that partial engagement of the slips against the casing string may result in the casing slipping from the tool and dropping into the well bore causing significant down time and repair.
Further, with the advent of tubing of high chromium content, the surface damage caused by slips has become undesirable because it can lead to unacceptable stress concentrations and stress corrosion in sour well conditions. There is therefore a need for an elevator apparatus and method of operation that can hold and manipulate tubing without significantly damaging the surface of the tubing and that eliminates the risk in traditional systems of engaging the tubing collar with resultant loss of “grip”.